A device for measuring in situ the velocity of a fluid flow, thus the fluid flow rate of a fluid flowing in a well-bore is known in the art. The flow measurement can be based on the measurements of the speed of rotation of an impeller, or a spinner. The speed of rotation of the spinner can be related to the amount of fluid passing through the measuring device. There are several types of spinner: a helical spinner, a vane-like spinner, a full-bore spinner or various types of flow-concentrating or diverter spinners. While the spinner is the most common flow-meter, torque flow-meters and cross-correlation flow-meters can also be used.
For example, the patent JP 8165879 describes a bore-hole flow velocity measuring device. The measuring device measures the velocity of a high-pressure and high-temperature fluid flowing into the bore-hole. The measuring device comprises a propeller positioned within the flowing fluid. The fluid velocity is converted into the rotation of the propeller which is transmitted to a slit disk. The slit disk interrupts the light fed through an optical path. The optical path is constituted of a first optical fiber, a first lens, a glass window provided on a pressure container, a reflector, a second lens, and a second optical fiber. The slit disk converts the light into an intermittent modulating signal of light which is provided to a photo-detector. The intermittent modulating signal of light is converted into an electrical pulse signal. The fluid velocity is measured by counting the number of pulse signal per time unit.
This measuring device fails to give indication regarding the direction of the flowing fluid and is not accurate in particular situation, e.g. low speed flow regime, erratic flow regime, etc. . . .